Not Applicable.
Not Applicable.
A method and apparatus for automatically maintaining two-phase entrainment flow of liquid from a well or reservoir while preventing flow stoppage from problems such as liquid-filled pipes, deadhead conditions, choking or dry recovery.
Contaminated properties are commonly remediated by extracting contaminated groundwater from the subsurface using entrainment methods. The simplest approach to liquid entrainment involves connecting a vacuum blower or vacuum pump to a well to simultaneously extract liquid and gases from the well (Hess et al., U.S. Pat. Nos. 5,050,676 and 5,197,541). However, this technique provides poor liquid entrainment unless high vacuums are used and the water table is relatively shallow. The more common technique of entrainment involves connecting a vacuum pump or vacuum blower to an entrainment tube that is extended into a well just above or slightly below the water table for recovery of fluids and gases (Salotti et al., U.S. Pat. No. 6,024,868; Mancini et al., U.S. Pat. Nos. 5,358,357 and 5,464,309; Knopik, U.S. Pat. No. 4,323,122; and Hajali et al., U.S. Pat. No. 5,172,764). When the vacuum pump or blower is turned on, the liquid is pulled into the pipe by vacuum and carried through the pipe by entrainment. The technical concepts of two-phase entrainment flow have been the focus of much historical experimentation and theoretical study. The concepts are summarized in Perry""s Chemical Engineering Handbook, Sixth Edition (1984) on pages 5-40 to 5-48. The theory and design concepts of two-phase entrainment will not be explained in detail herein since the concepts are used in common practice and are well understood by those skilled in the art.
Perry""s Chemical Engineering Handbook describes several ranges oftwo-phase flow that are classified based on the gas-to-liquid ratio maintained during transfer. Most remedial systems typically tend to operate in the range of annular flow or slug flow. This means that most remedial liquid entrainment methods operate at liquid-to-gas ratios of less than 0.25 gallons of liquid per cubic feet of gas and at entrainment velocities greater than 900 feet per minute. The successful operation of a remedial entrainment system often relies on the ability to maintain these liquid-to-gas relationships. The most common form of gas recovery in remedial systems is air.
Groundwater elevation fluctuations occur at many remediation sites due to precipitation and changes in barometric pressure. At low groundwater elevation conditions, the water table falls below the elevation of the entrainment tube so that water entrainment cannot occur, thus resulting in dry recovery. Dry recovery refers to the recovery of gas with no entrained liquids. At high water table conditions, the elevation of the groundwater covers the end of the vacuum entrainment tube with water, thus making it impossible for the pipe to recover air. When the bottom of the entrainment pipe is covered with water, the vacuum inside the entrainment tube will pull water up into the pipe to an elevation where the head of water is equivalent to the lift vacuum. This phenomena is often referred to as a xe2x80x9cdeadheadxe2x80x9d condition. In other instances of high water table conditions, the entrainment system may be able to keep up with the increased rate of water recovery for a period of time, only to eventually shutdown due to flooded pipes and manifolds. This phenomena is referred to as xe2x80x9cchoking.xe2x80x9d Deadhead conditions and choking are common in remedial systems that rely on entrainment recovery techniques. These conditions are the cause of excessive system down-time and increased operational costs for many remedial systems.
Remedies to correct deadhead and choking conditions have been attempted such as placing holes or vacuum relief valves into the sides of the entrainment tube. These methods, however, have been largely unsuccessful. Entrainment tubes with side holes tend to allow air to flow preferentially through the unrestricted side openings without allowing for entrainment of water at the bottom of the tube. In designs with a side-mounted vacuum relief valve, the vacuum required to open the valve tends to maintain xe2x80x9cdeadheadxe2x80x9d conditions at the bottom of the entrainment tube, thus resulting in only dry recovery. Entrainment systems that rely on void-space buoyancy have failed by fluid displacement within the voids.
Entrainment systems have been devised where air is injected or introduced into a well to enhance the gas-to-liquid ratio and prevent deadhead conditions (Salotti et al., U.S. Pat. No. 6,024,868; Mancini et al., U.S. Pat. Nos. 5,358,357 and 5,464,309; Hess et al., U.S. Pat. No. 5,197,541; and Hajali et al., U.S. Pat. No. 5,172,764). In the alternative, Hess et al. in U.S. Pat. No. 5,197,541 requires a second air injection well to enhance subsurface gas-to-liquid ratios. However, these systems are ineffective where there is large fluctuations in the groundwater table or for highly permeable soils where the introduced air cannot adequately compensate for the increased groundwater flow into the well.
Complex electronic control systems have also been devised in an attempt to better control the gas-to-liquid recovery ratios in order to maintain an operable system (Salotti et al., U.S. Pat. No. 6,024,868 and Wells, U.S. Pat. No. 4,844,797). However, these systems are complex, expensive and time-consuming to install. Furthermore, they do not resolve the complex problem of creating a system that functions with widely fluctuating water tables.
Finally, others have resorted to systems that separately recover liquid and gas from the well in order to avoid the complications of fluid entrainment (Lynch, U.S. Pat. No. 5,271,467 and Croy, U.S. Pat. No. 5,380,125). Croy uses an inflatable packer to separate the liquid and gas systems, and includes separate piping for the gas and liquid so liquid entrainment is not required. Lynch uses ejector pumps to remove the liquids from the well while a blower or fan is used to remove the gases. Neither of systems solve the complexities associated with two-phase entrainment flow.
It would be desirable to have a liquid entrainment device that moves up and down with the water table and is capable of self-regulating the rate of liquid and gas recovery for extended periods of time without complex electronics or injected air. This system could solve the reoccurring problems associated with deadhead conditions, choking, and dry recovery.
This invention describes an apparatus and means to entrain liquids from a well or reservoir by the use of a buoyant device that moves with the elevation of the water, thus eliminating the problems associated with deadhead conditions, choking and dry recovery.
Accordingly, several objects and advantages of our invention are:
(a) the invention provides an apparatus that recovers liquids by entrainment without experiencing deadhead conditions, choking or dry recovery due to fluctuations in the elevation of the liquid level;
(b) the invention provides an apparatus in which the rate of recovery of gas and liquid are maintained at a stable rate to assure that the proper gas-to-liquid ratios are maintained for two-phase conveyance of liquids;
(c) the invention provides an apparatus for two-phase liquid recovery without the need for manual adjustments or electronically controlled devices to regulate the gas-to-liquid ratio and maintain entrainment of liquids;
(d) the invention includes a transition member at the location where the gas and liquid are mixed that is capable of producing secondary venturi vacuum effects to provide for liquid lift not accomplished by ordinary two-phase extraction systems; and
(e) the invention maintains the gas recovery point above the level of the liquid at all times to eliminate deadhead conditions.